[tech] problems with TV-out

[Duncan Sargeant]

Anil Sharma wrote on Wed February 04, at 21:07 +0800:
> I have a Geforce 2 and it displays perfectly to my TV through an composite 
> cable with just the OS (XP) desktop showing.  However, when playing movies 
> onto the TV there appears out of nowhere lots of horizontal lines --- which 
> get especially bad with block colour (like in Astroboy *sobs*).  This 
> happens with DVD, DIVX and even Real Media clips.  It isn't a zero 
> groun-loop problem.  I was thinking it is interference... but why would it 
> not manifest itself with block colour from displaying the desktop?
> 
> Any ideas?

Yeah.  I saw it and its the same thing I get on my nvidia GeForce 256
card.  Its all in the overscan.

The BUGS file from the nvtv tool has this to say:

* Especially in the Brooktree Huge modes, there are CRT values that allow 
  doubleview, but there is not enough time to draw the hardware cursor
  in these cases. That may cause a system freeze. (Disabling the
  hardware cursor in XF86Config helps in those cases). Even without
  hardware cursor, sometimes the system freezes.

* There are similar problems with the Chrontel PAL 800x600 Large mode:
  I have sometimes experienced a system freeze, and the TV color flickers
  since it seems not to be able to produce the data in time, so the
  color information is shifted for half a pixel. (Color data is latched
  on two subsequent clocks).

The first point isn't relevant, but the 2nd looks odd without it. 
The easy way to test this is to change the modes and see what
happens.  Try the 640x480 modes, and try the smaller 800x600 modes, and
compare with the large 800x600 mode.  I tested this with
"xsetroot -solid red" using different colours.  Most affected are
red,green,blue (0xff0000 out-of-sync will give a black 0x000000 pixel
most of the time), and magenta,cyan give lighter gray lines.  Note that
any graycolour is unaffected (0xXYXYXY shifts to give itself at least
half of the time)

The extra hint is that 768x576 is actually based on the abovementioned
large 800x600 mode.  I suspect you're not noticing it with the desktop
background because its not going into the 800x600 large mode, but movie
players tend to put the TV-out into PAL mode.

NTSC probably doesn't have this problem because its a smaller
resolution.

,dunc